This invention relates to a vane compressor which is reduced in weight by forming vanes, a cylinder block, a rotor, side blocks, etc. thereof from an aluminum-based alloy (hereinafter referred to as "an aluminum alloy").
A vane compressor in general comprises a cylinder block having a camming inner peripheral surface of a substantially elliptical cross-section, a pair of side blocks closing front and rear open ends of the cylinder block to form a cylinder, a rotor rotatably received within the cylinder, and a plurality of vanes slidably fitted in respective vane slits formed in the outer peripheral surface of the rotor to be urged against the inner peripheral surface of the cylinder block to divide the interior of the cylinder into compression chambers which are varied in volume with rotation of the rotor, whereby a refrigerant gas drawn into the compression chambers is compressed.
Recently, many vane compressors are made from aluminum alloys instead of iron-based alloys in order to reduce their weights. For example, vane compressors of this type have been proposed by Japanese Utility Model Publication (Kokoku) No. 50-33712, and Japanese Provisional Patent Publication (Kokai) No. 62-60993.
According to the vane compressor proposed by the Japanese Kokoku, vanes are formed of an aluminum alloy for weight-reducing purpose, and the surfaces of the vanes are anodized to have aluminum oxide films coated thereon while being impregnated with polytetrafluoroethylene (PTFE) in order to improve the anti-seizure and wear resistance. According to the vane compressor proposed by the Japanese Kokai, the sliding surfaces of the vanes are coated with a Ni-based alloy material containing ceramic powder as a disperse phase to impart excellent anti-seizure and wear resistance to the compressor.
These proposed vane compressors have attained weight reduction by the use of a light metal, i.e. an aluminum alloy. However, in the above conventional compressor disclosed by the Japanese Kokoku, the anodic coating film, i.e. the aluminum oxide film coated over the vanes is basically of the same kind material as the material forming the surfaces of the cylinder block, rotor, etc. against which the vanes slide, and therefore, cannot give sufficient slidability, wear resistance, and durability. In the above conventional compressor disclosed by the Japanese Kokai, due to the ceramic dispersed in the Ni-based alloy coating material, the coating film is very hard, showing, for example, Hv=3000-3500 in the case of the ceramic being SiC, Hv=2800-3800 in the case of the ceramic being TiC, and Hv=2400-2800 in the case of the ceramic being Si.sub.3 N.sub.4. Therefore, the coating film has low abrasiveness, so that it takes much time to grind the film, resulting in a shortened life of the abrasive grinder, as well as poor productivity. Further, although it has also been employed to coat compressor component parts with iron, this suffers from low stability in the thickness of a film formed by the coating, requiring finishing of the film after the coating, which results in increased manufacturing cost. Further, the adhesion of the film to the aluminum alloy is lower due to repetition of thermal shock during operation of the compressor, leading to a shortened life of the vanes.